1. Field of the Invention
The present invention relates to a thin metallic layer type magnetic recording medium suitable for high density magnetic recording.
2. Description of the Prior Arts
Recently, high density magnetic recording technology has been especially developed because of improvements of a recording and reproducing system, a running system and a magnetic head of a magnetic recording apparatus and a magnetic recording medium. Among them, the requirement for high density magnetic recording in magnetic recording media has been attained mainly by an increase of a coercive force and an increase of a residual magnetic flux density to reduce a thickness of the magnetic recording medium. However, in the conventional magnetic recording media prepared by using a magnetic powder and an organic binder, it has been also impossible to increase the residual magnetic flux density over 3,000-4,000 gauss. Thus, the improvement of the magnetic recording density is limited. Thus, a thin metallic layer type magnetic recording media prepared without any organic binder have been considered to be important. The thin metallic layer type magnetic recording media have been prepared by forming a thin metallic layer on a substrate by forming metallic particles made of a metal or alloy of iron group element or an alloy thereof with a third element by a vacuum evaporation. sputtering, ion-plating, ion beam evaporation or electrochemical method and depositing the metallic particles on the non-magnetic substrate. Among these methods, the vacuum evaporation method has been especially developed as the technology for preparing uniform, long magnetic recording media in an industrial scale.
It has been known that the characteristic of the thin magnetic layer formed by the vacuum evaporation method is mainly dependent upon the magnetic characteristics thereof. In order to attain high recording density, it has been required to have high coercive force.
The following methods have been proposed to increase a coercive force in the vacuum evaporation method.
(a) a tilt deposition; PA1 (b) a deposition in a magnetic field; PA1 (c) a control by a selection of a material for a base; and PA1 (d) a crystalline growth by a heat treatment.
Among these methods, the most effective practical method is the tilt deposition process disclosed in Japanese Examined Patent Publication No. 19389/1966. In this process, as shown in FIG. 1, a thin metallic layer is formed by a tilt deposition of a metallic particles (1) at a tilt angle .theta. to the normal line (3) on a surface of a substrate (2). This is especially advantageous method in the inventors' experiments. In the tilt deposition, the thin magnetic layer can be formed as a cobalt-nickel type alloy thin magnetic layer, because of excellent magnetic characteristics thereof. In the tilt deposition, however, it is required to reduce the tilt angle .theta. so as to increase the deposition efficiency. The effect of the tilt deposition is reduced by lowering the tilt angle .theta.. Therefore, the conventional cobalt-nickel type alloy thin magnetic layer has not been satisfactory in the practical purpose.